1. Field of the Invention
The field of the invention is data processing, or, more specifically, methods, apparatus, and products for controlling data flow through a data communications link.
2. Description of Related Art
The development of the EDVAC computer system of 1948 is often cited as the beginning of the computer era. Since that time, computer systems have evolved into extremely complicated devices. Today's computers are much more sophisticated than early systems such as the EDVAC. Computer systems typically include a combination of hardware and software components, application programs, operating systems, processors, buses, memory, input/output devices, and so on. As advances in semiconductor processing and computer architecture push the performance of the computer higher and higher, more sophisticated computer software has evolved to take advantage of the higher performance of the hardware, resulting in computer systems today that are much more powerful than just a few years ago.
One of the areas that has seen considerable advance is data communications, although there is still need for improvements in the area. Some data communications protocols, including the IEEE 802.1x protocols, for example, define a rudimentary flow control mechanisms. These are typically based on an “x-on” and “x-off” scheme where, if a receiver becomes congested, the receiver can send a frame back to the originator, a flow control message, which shuts off all communications for a period of time defined in the flow control message. The disadvantage of this scheme is that all sessions running on a given data communications link are interrupted to provide flow control. Sessions with both high and low latency requirements are all interrupted. Sessions which are streaming video/audio information risk harmful interruptions, possibly yielding visible dropouts in the video/audio stream. This x-on/x-off technique does alleviate network congestion—but at the very high price of interrupting all communications sessions on a link regardless of the particular data communications requirements or priorities any particular communications session may be. This means that networks must be over-designed to have lots of additional bandwidth to make sure the flow control is invoked as infrequently as possible.